The present invention relates to a surge arrester for shunting electrical surges to ground. More particularly, the surge arrester of the present invention may have a disconnect which disconnects the surge arrester from ground in the event of a failure of the surge arrester.
Over voltage surges, which travel along an electric power distribution system and which are not properly averted or diverted, often damage transformers and other electrical equipment of the electric power distribution system, as well as the electrical equipment of residential, commercial and industrial customers supplied by the electric power distribution system. Consequently, surge arresters are commonly used in an electric power distribution system for shunting over voltage surges to system ground before the over voltage surges can damage the electrical equipment connected in, or to, the electric power distribution system.
Typical surge arresters used in electric power distribution systems can fail in a runaway condition. When such a failure occurs, the surge arrester may explode apart, potentially damaging nearby equipment and injuring anyone who happens to be near. Therefore, it has been a common prior art practice to provide surge arresters with fault disconnectors that open the circuits containing failed surge arresters. Usually, a fault disconnector is connected between its corresponding surge arrester and ground so that, when the fault disconnector activates upon failure of the surge arrester, the fault disconnector separates the surge arrester from its ground connection. The separated ground connection not only disconnects the failed,surge arrester from the electric power distribution system, but also provides a visible indication to a utility linesman that the surge arrester has failed.
A typical fault disconnector includes a cartridge, which may contain a predetermined amount of gun powder, and which is heated as the surge arrester begins to fail. When the cartridge heats sufficiently, it explodes separating the surge arrester from its ground connection. The amount of gun powder that is used in the cartridge is sufficient to cause such separation but not sufficient to cause damage or injury.
The cartridge, and the other elements of the fault disconnector, are contained within a disconnector housing that is a separate component of the surge arrester. The disconnector housing has an internally threaded hole for threaded attachment to the surge arrester, and has an external threaded ground connector, for attachment to a ground lead. An electrical resistor, which is another element of the fault disconnector and which is housed by the disconnector housing, is electrically connected between a surge arrester terminal and the ground connector, of the disconnector. Accordingly, when the surge arrestor fails, the current through the electrical resistor increases abnormally and generates enough heat to trigger the cartridge causing it to break the disconnector housing and to separate the ground terminal from the surge arrester.
The use of a separate disconnector housing increases the part count of a surge arrester which, in turn, increases the manufacturing cost of the surge arrester. The invention disclosed in U.S. application Ser. No. 08/954,987 filed on Oct. 21, 1997 now U.S. Pat. No. 5,923,518, is directed to a surge arrester which reduces part count by housing the fault disconnector in an end cap of a surge arrester.
The present invention is a further improvement and is directed to a surge arrester in which the fault disconnector is housed in a cavity formed between the end cap and the mounting bracket. This arrangement makes the surge arrester easier to automate its assembly and/or reduces voids in the disconnector housing so that air holes are reduced when the end of the surge arrester is potted.
In accordance with one aspect of the present invention, a surge arrester comprises a mounting bracket, a surge arresting element, an end cap, and a fault disconnector. The mounting bracket has a bracket recess. The surge arresting element is arranged to break down and conduct in the presence of a surge. The end cap is electrically coupled to the surge arresting element. The end cap has a cap recess, and the end cap is received by the mounting bracket so that the bracket recess and the cap recess cooperate to form a housing cavity therebetween. The fault disconnector is arranged to disconnect the surge arresting element from an electrical line in the event of a fault, and the fault disconnector is at least partially housed within the housing cavity.
In accordance with another aspect of the present invention, a surge arrester comprises a mounting bracket, a surge arresting element, a conductive end cup, and a fault disconnector. The mounting bracket forms a bracket cup having a bottom and a cup wall. The surge arresting element is arranged to conduct in the presence of a surge. The conductive end cup is electrically coupled to the surge arresting element, and the conductive end cup has a bottom and an end cup wall. The bracket cup is housed within the conductive end cup. The fault disconnector is arranged to disconnect the surge arresting element from an electrical line in the event of a fault, and the fault disconnector is at least partially housed within the bracket cup.
In accordance with yet another aspect of the present invention, a surge arrester comprises a mounting bracket, a surge arresting element, an electrically conductive connector, and a fault disconnector. The mounting bracket has first and second bracket walls. The first and second bracket walls form an opening therebetween, and the second bracket wall is attached to the first bracket wall by at least one bridge. The surge arresting element is arranged to conduct in the presence of a surge. The electrically conductive connector is electrically coupled to the surge arresting element, and the electrically conductive connector has a connector wall forming a connector recess. The connector wall has at least one slot. The electrically conductive connector is received by the mounting bracket so that the connector wall is received in the opening, so that the second bracket wall is received within the connector wall, and so that the bridge is received in the slot. The fault disconnector is arranged to disconnect the surge arresting element from an electrical line in the event of a fault. The fault disconnector is housed within the second bracket wall of the mounting bracket.